The recent global outbreak of influenza A caused by a novel swine-origin H1N1 influenza A virus (S-OIV) has led to a growing concern regarding the pandemic potential of the highly pathogenic avian influenza (HPAI) H5N1 viruses because the currently licensed seasonal influenza vaccines fail to produce cross-protection against the newly emerging influenza A viruses (IAVs). Therefore, development of a safe and effective vaccine against divergent IAVs, especially those causing current and future influenza pandemics, is urgently needed. We and others have reported that the extracellular domain of matrix protein 2 (M2e) and the fusion peptide (FP) of the hemagglutinin-2 (HA2) that contain highly conserved epitopes can induce strong humoral and cellular immune responses and broad protection against IAVs. Our preliminary studies also showed that the recombinant HA protein fused to Fc fragment of IgG as an immune enhancer could induce strong cross-neutralizing antibody responses and cross- protection against various strains of H5N1 viruses. We thus hypothesize that a recombinant protein containing the highly conserved epitopes in M2e and FP fused to Fc may elicit potent humoral and cellular immune responses, including the neutralizing antibodies, and induce cross-protection against divergent IAVs, including current epidemic H1N1 and HPAI H5N1 strains, and other isolates that might cause future pandemics. The specific aims of this proposal are: (1) to design an influenza vaccine containing conserved epitopes in M2e and FP of IAV (M2e-FP) fused with Fc immune enhancer (M2e-FP-Fc) and use M2e-FP, FP-Fc and M2e-Fc as controls; (2) to immunize mice and rabbits with these antigens, alone or in combination (e.g., M2e-FP-Fc + FP-Fc), and to assess specific humoral and cellular immune responses and neutralizing antibodies in the vaccinated animals; (3) to evaluate the in vivo protective immunity against IAV challenge in the immunized mouse models. The long-term goal of the proposed study is to develop a universal influenza A vaccine against divergent IAVs, including those causing future influenza pandemics. PUBLIC HEALTH RELEVANCE: The current H1N1 influenza pandemic (commonly known as the swine flu) and the potential outbreak of H5N1 influenza in the future pose serious threats to public health worldwide. The goal of this proposed study is to design and develop a universal vaccine for influenza A viruses based on the conserved sequences of viral surface proteins linked with a molecule to enhance immunogenicity of the antigens and this influenza vaccine is expected to be effective and safe for human use for preventing influenza epidemics in the future.